The eyes suppress a circadian rhythm of FOS expression in the suprachiasmatic nucleus in the absence of light

Dietary Oat β-Glucan Alleviates High-Fat Induced Insulin Resistance through Regulating Circadian Clock and Gut Microbiome

SCOPE

High-fat diet induced circadian rhythm disorders (CRD) are associated with metabolic diseases. As the main functional bioactive component in oat, β-glucan (GLU) can improve metabolic disorders, however its regulatory effect on CRD remains unclear. In this research, the effects of GLU on high-fat diet induced insulin resistance and its mechanisms are investigated, especially focusing on circadian rhythm-related process.

METHODS AND RESULTS

Male C57BL/6 mice are fed a low fat diet, a high-fat diet (HFD), and HFD supplemented 3% GLU for 13 weeks. The results show that GLU treatment alleviates HFD-induced insulin resistance and intestinal barrier dysfunction in obese mice. The rhythmic expressions of circadian clock genes (Bmal1, Clock, and Cry1) in the colon impaired by HFD diet are also restored by GLU. Further analysis shows that GLU treatment restores the oscillatory nature of gut microbiome, which can enhance glucagon-like peptide (GLP-1) secretion via short-chain fatty acids (SCFAs) mediated activation of G protein-coupled receptors (GPCRs). Meanwhile, GLU consumption significantly relieves colonic inflammation and insulin resistance through modulating HDAC3/NF-κB signaling pathway.

CONCLUSION

GLU can ameliorate insulin resistance due to its regulation of colonic circadian clock and gut microbiome.

Retinal Circadian Clocks and Control of Retinal Physiology

Retinas of all classes of vertebrates contain endogenous circadian clocks that control many aspects of retinal physiology, including retinal sensitivity to light, neurohormone synthesis, and cellular events such as rod disk shedding, intracellular signaling pathways, and gene expression. The vertebrate retina is an example of a “peripheral” oscillator that is particularly amenable to study because this tissue is well characterized, the relationships between the various cell types are extensively studied, and many local clock-controlled rhythms are known. Although the existence of a photoreceptor clock is well established in several species, emerging data are consistent with multiple or dual oscillators within the retina that interact to control local physiology. Aprominent example is the antiphasic regulation of melaton in and dopamine in photoreceptors and inner retina, respectively. This review focuses on the similarities and differences in the molecular mechanisms of the retinal versus the SCN oscillators, as well as on the expression of core components of the circadian clockwork in retina. Finally, the interactions between the retinal clock(s) and the master clock in the SCN are examined.

Can sleep quality and wellbeing be improved by changing the indoor lighting in the homes of healthy, elderly citizens?

The study investigated the effect of bright blue-enriched versus blue-suppressed indoor light on sleep and wellbeing of healthy participants over 65 years. Twenty-nine participants in 20 private houses in a uniform settlement in Copenhagen were exposed to two light epochs of 3 weeks with blue-enriched (280 lux) and 3 weeks blue-suppressed (240 lux) indoor light or vice versa from 8 to 13 pm in a randomized cross-over design. The first light epoch was in October, the second in November and the two light epochs were separated by one week. Participants were examined at baseline and at the end of each light epoch. The experimental indoor light was well tolerated by the majority of the participants. Sleep duration was 7.44 (95% CI 7.14-7.74) hours during blue-enriched conditions and 7.31 (95% CI 7.01-7.62) hours during blue-suppressed conditions (p = 0.289). Neither rest hours, chromatic pupillometry, nor saliva melatonin profile showed significant changes between blue-enriched and blue-suppressed epochs. Baseline Pittsburgh Sleep Quality Index (PSQI) was significantly worse in females; 7.62 (95% CI 5.13-10.0) versus 4.06 (95% CI 2.64-5.49) in males, p = 0.009. For females, PSQI improved significantly during blue-enriched light exposure (p = 0.007); no significant changes were found for males. The subjective grading of indoor light quality doubled from participants habitual indoor light to the bright experimental light, while it was stable between light epochs, although there were clear differences between blue-enriched and blue-suppressed electrical light conditions imposed. Even though the study was carried out in the late autumn at northern latitude, the only significant difference in Actiwatch-measured total blue light exposure was from 8 to 9 am, because contributions from blue-enriched, bright indoor light were superseded by contributions from daylight.

Unilateral anterior ischemic optic neuropathy: chromatic pupillometry in affected, fellow non-affected and healthy control eyes

The intrinsically photosensitive retinal ganglion cells (ipRGCs) express the photopigment melanopsin, which is sensitive to blue light. Previous chromatic pupillometry studies have shown that the post-illumination response is considered an indicator of the melanopsin activation. The aim of this study was to investigate the ipRGC mediated pupil response in patients with a unilateral non-arteritic anterior ischemic optic neuropathy (NAION). Consensual pupil responses during and after exposure to continuous 20 s blue (470 nm) or red (660 nm) light of high intensity (300 cd/m(2)) were recorded in each eye for 10 patients. Comparisons were performed both intra-individually (affected versus non-affected eyes) and inter-individually (compared with healthy controls). The pupil response was calculated both during the illumination and during the post-illumination phase. The pupil responses to blue and red colors were significantly reduced in the NAION-affected eyes, compared with the fellow non-affected eyes. When comparing the affected eyes with the healthy control eyes, the post-illumination responses were not significantly different. In addition, the post-illumination pupil responses after blue light exposure were increased in the fellow non-affected patients' eyes, compared with the healthy controls. However, significance was only reached for the late post-illumination response. In conclusion, chromatic pupillometry disclosed reduced post-illumination pupil responses in the NAION-affected eyes, compared with the non-affected fellow eyes, suggesting dysfunction of the ipRGCs. Compared with the responses of the healthy controls, the blue light post-illumination pupil responses were similar in the affected eyes and increased in the fellow non-affected eyes. This suggests a possible adaptive phenomenon, involving the ipRGCs of both eyes after unilateral NAION.

Physiology of circadian entrainment

Mammalian circadian rhythms are controlled by endogenous biological oscillators, including a master clock located in the hypothalamic suprachiasmatic nuclei (SCN). Since the period of this oscillation is of approximately 24 h, to keep synchrony with the environment, circadian rhythms need to be entrained daily by means of Zeitgeber ("time giver") signals, such as the light-dark cycle. Recent advances in the neurophysiology and molecular biology of circadian rhythmicity allow a better understanding of synchronization. In this review we cover several aspects of the mechanisms for photic entrainment of mammalian circadian rhythms, including retinal sensitivity to light by means of novel photopigments as well as circadian variations in the retina that contribute to the regulation of retinal physiology. Downstream from the retina, we examine retinohypothalamic communication through neurotransmitter (glutamate, aspartate, pituitary adenylate cyclase-activating polypeptide) interaction with SCN receptors and the resulting signal transduction pathways in suprachiasmatic neurons, as well as putative neuron-glia interactions. Finally, we describe and analyze clock gene expression and its importance in entrainment mechanisms, as well as circadian disorders or retinal diseases related to entrainment deficits, including experimental and clinical treatments.

Elevated mPer1 gene expression in tumor stroma imaged through bioluminescence

The tumor stroma has significant effects on cancer cell growth and metastasis. Interactions between cancer and stromal cells shape tumor progression through poorly understood mechanisms. One factor regulating tumor growth is the circadian timing system that generates daily physiological rhythms throughout the body. Clock genes such as mPer1 serve in molecular timing events of circadian oscillators and when mutated can disrupt circadian rhythms and accelerate tumor growth. Stimulation of mPer1 by cytokines suggests that the timing of circadian oscillators may be altered by these tumor-derived signals. To explore tumor and stromal interactions, the pattern of mPer1 expression was imaged in tumors generated through subcutaneous injection of Lewis lung carcinoma (LLC) cells. Several imaging studies have used bioluminescent cancer cell lines expressing firefly luciferase to image tumor growth in live mice. In contrast, this study used non-bioluminescent cancer cells to produce tumors within transgenic mice expressing luciferase controlled by the mPer1 gene promoter. Bioluminescence originated only in host cells and was significantly elevated throughout the tumor stroma. It was detected through the skin of live mice or by imaging the tumor directly. No effects on the circadian timing system were detected during three weeks of tumor growth according to wheel-running rhythms. Similarly, no effects on mPer1 expression outside the tumor were found. These results suggest that mPer1 activity may play a localized role in the interactions between cancer and stromal cells. The effects might be exploited clinically by targeting the circadian clock genes of stromal cells.

Temporally restricted role of retinal PACAP: integration of the phase-advancing light signal to the SCN

Circadian rhythms in physiology and behavior are temporally synchronized to the day/night cycle through the action of light on the circadian clock. In mammals, transduction of the photic signal reaching the circadian oscillator in the suprachiasmatic nucleus (SCN) occurs through the release of glutamate and pituitary adenylate cyclase-activating peptide (PACAP). The authors' study aimed at clarifying the role played by PACAP in photic resetting and entrainment. They investigated the circadian response to light of PACAPnullmice lacking the 5th exon of the PACAP coding sequence. Specifically, they examined free-running rhythms, entrainment to 12-h light:12-h dark (LD)cycles, the phase-response curve (PRC) to single light pulses, entrainment to a23-h T-cycle, re-entrainment to 6-h phase shifts in LD cycles, and light-induced c-Fos expression. PACAP-null and wild-type mice show similar free-running periods and similar entrainment to 12:12 LD cycles. However, the PRC of PACAP-null mice lacks a phase-advance portion. Surprisingly, despite the absence of phase advance to single light pulses, PACAP-null mice are able to entrain to a 23-h T-cycle, but with a significantly longer phase angle of entrainment than wild types. In addition, PACAP-null mice re-entrain more slowly to a 6-h phase advance of the LD cycle. Nevertheless, induction of c-Fos by light in late night is normal. In all experiments, PACAP-null mice show specific behavioral impairments in response to phase-advancing photic stimuli. These results suggest that PACAP is required for the normal integration of the phase advancing light signal by the SCN.

Transcriptional Profiling of Circadian Patterns of mRNA Expression in the Chick Retina

Previous transcriptome analyses have identified candidate molecular components of the avian pineal clock, and herein we employ high density cDNA microarrays of pineal gland transcripts to determine oscillating transcripts in the chick retina under daily and constant darkness conditions. Subsequent comparative transcriptome analysis of the pineal and retinal oscillators distinguished several transcriptional similarities between the two as well as significant differences. Rhythmic retinal transcripts were classified according to functional categories including phototransductive elements, transcription/translation factors, carrier proteins, cell signaling molecules, and stress response genes. Candidate retinal clock transcripts were also organized relative to time of day mRNA abundance, revealing groups accumulating peak mRNA levels across the circadian day but primarily reaching peak values at subjective dawn or subjective dusk. Comparison of the chick retina transcriptome to the pineal transcriptome under constant conditions yields an interesting group of conserved genes. This group includes putative clock elements cry1 and per3 in addition to several previously unidentified and uninvestigated genes exhibiting profiles of mRNA abundance that varied markedly under daily and constant conditions. In contrast, many transcripts were differentially regulated, including those believed to be involved in both melatonin biosynthesis and circadian clock mechanisms. Our results indicate an intimate transcriptional relationship between the avian pineal and retina in addition to providing previously uncharacterized molecular elements that we hypothesize to be involved in circadian rhythm generation.

A circadian rhythm in the expression of PERIOD2 protein reveals a novel SCN-controlled oscillator in the oval nucleus of the bed nucleus of the stria terminalis

Circadian rhythms in mammals are regulated not only globally by the master clock in the suprachiasmatic nucleus (SCN), but also locally by widely distributed populations of clock cells in the brain and periphery that control tissue-specific rhythmic outputs. Here we show that the oval nucleus of the bed nucleus of the stria terminalis (BNST-OV) exhibits a robust circadian rhythm in expression of the Period2 (PER2) clock protein. PER2 expression is rhythmic in the BNST-OV in rats housed under a light/dark cycle or in constant darkness, in blind rats, and in mice, and is in perfect synchrony with the PER2 rhythm of the SCN. Constant light or bilateral SCN lesions abolish the rhythm of PER2 in the BNST-OV. Large abrupt shifts in the light schedule transiently uncouple the BNST-OV rhythm from that of the SCN. Re-entrainment of the PER2 rhythm is faster in the SCN than in the BNST-OV, and it is faster after a delay than an advance shift. Bilateral adrenalectomy blunts the PER2 rhythm in the BNST-OV. Thus, the BNST-OV contains circadian clock cells that normally oscillate in synchrony with the SCN, but these cells appear to require both input from the SCN and circulating glucocorticoids to maintain their circadian oscillation. Taken together with what is known about the functional organization of the connections of the BNST-OV with systems of the brain involved in stress and motivational processes, these findings place BNST-OV oscillators in a position to influence specific physiological and behavioral rhythms downstream from the SCN clock.